1. Field of the Invention
The present invention relates to an image forming apparatus including a process cartridge which is detachably mountable to a main assembly of the image forming apparatus, particularly an image forming apparatus which permits data communication between a non-contact memory mounted process cartridge and the apparatus main assembly.
2. Background Art
For example, in an ordinary image forming apparatus, such as a copying machine, a printer or the like, a load unit constituting a part of an image forming means, such as a photosensitive drum or an intermediary transfer belt, is rotationally driven by transmitting thereto a driving force (power) through a coupling or connection mechanism disposed between such a load unit and a driving source of the main assembly of the image forming apparatus. Such a load unit reaches the end of its life due to wear and/or deterioration with time. The life of the load unit is shorter than that of the image forming apparatus main assembly, so that there is a need for the load unit to be replaced with a new one on several occasions until the image forming apparatus main assembly reaches the end of its life. For this reason, the load unit is used in the form of a cartridge in view of the ease in mounting and dismounting the cartridge in many cases.
In recent years, a memory has been provided in the cartridge so as to have the following functions (1), (2) and (3):
(1) in the memory, data, such as initial characteristics of the unit at the time of the production thereof, identifying (discriminating) information thereof, or the like is stored, and the data is used for switching control specifications for the photosensitive drum, or the like in the cartridge;
(2) in the memory, data on an operation time of the unit is stored and used for judging the unit's replacement timing; and
(3) in the memory, the same fluctuation values vary, depending on durability factors of the unit, and optimum image formation is performed on the basis of the most up-to-date values.
As a result, the memory is utilized for improving image qualities of the image forming apparatus.
As the memory for such a purpose, a non-contact memory is used in many cases, since it has the advantages of, e.g., high reliability of point of contact attributable to high resistance to mounting/dismounting operations and a simple circuit structure. This is because, the non-contact memory carries out communication with the apparatus main assembly by transmission and reception of electromagnetic waves between antennas provided in both the apparatus main assembly and the memory, so that the non-contact memory does not need any contact between metal terminals as in a conventional memory, thus causing no problems arising from the required contact of terminals, such as noise, toner contamination, various vibrations, or the like.
With respect to the access procedure of the image forming apparatus to the non-contact memory provided in the memory as described above, Japanese Laid-Open Patent Application (JP-A) 2002-149039 has proposed that a state of means for transmitting electromagnetic waves to the non-contact memory is switched on the basis of a detection result determining whether a door is opened or closed, the door permitting a detachably mountable load unit to be mounted to and dismounted from an apparatus main assembly. In other words, when the door is opened, communication is stopped since there is a possibility that the load unit is removed, and on the other hand, when the door is closed, the communication is started since there is a possibility that the load unit is mounted.
However, in the case where the load unit is mounted at the time when the door is closed, the state in which communication is permitted with reliability is not necessarily optimal. When a user mounts the load unit into the apparatus main assembly by opening the door, it is by no means easy to mount the load unit at a predetermined position accurately at the time of image formation. This is because a drive portion of the load unit to be connected to the apparatus main assembly is required to be positioned with a high degree of accuracy. In other words, the allowance for positional deviation from the optimal position is very small.
On the other hand, a structure has been employed in which the apparatus main assembly is automatically moved to a predetermined position at the time of image formation by transmitting a driving force to the load unit in an image-forming operation so as to obviate the necessity for the user to take the trouble to accurately mount the load unit. Accordingly, somewhat of a positional deviation of the load unit with respect to the apparatus main assembly occurs immediately after the door is closed. As a result, an antenna on the load-unit side is not necessarily located in an ideal position.
To accommodate such positional deviation, the receiving sensitivity or the sending power of the antenna is increased in order to permit reliable communication before carrying out necessary operations for image formation. However, in this case, size reduction of the load unit becomes difficult, and there arises a possibility that an increase in sending powder causes interference with an antenna with which it is not intended to communicate or leakage of electromagnetic waves to the outside of the image forming apparatus in some cases. For this reason, in view of measures that can be taken against these problems, it cannot be said that communication is ensured even when the position of the load unit is somewhat deviated from the predetermined position.